Sintered refractories with coarse grains joined together by a matrix and comprising more than 85 wt. % of zirconia are used in applications in which good mechanical strength and high corrosion resistance are required at temperatures above 1800° C. Such products are notably recommended in incineration, glassmaking, petrochemistry, in reactors for manufacturing carbon black and in the cement industry, for protection against attack by corrosive agents such as slag, glass, or dust-laden smoke.
The structure of these products, combining coarse grains and a matrix, contributes decisively to the mechanical properties. Zirconia-based products with a very homogeneous structure, obtained conventionally from powders of particles smaller than 50 microns, are therefore considered to be unsuitable for these applications.
Moreover, sintered refractories comprising more than 85 wt. % of zirconia and with coarse grains bound by a matrix rich in zirconia generally have low resistance to thermal shock. In fact, to facilitate sintering, which is made difficult by the presence of coarse grains, conventionally at least 1% of silica is added, which is considered to have a harmful effect on resistance to thermal shock.
Alternatively, within the glassmaking and metallurgical industries, EP 0 404 610 discloses products that have coarse grains bound by a matrix, the matrix being formed from a powder comprising less than 1% of silica, and preferably being more or less silica-free, but necessarily comprising monoclinic zirconia. Above 1%, silica in fact leads, according to this document, to elimination of the beneficial effect of the monoclinic zirconia. However, the low silica content makes sintering more difficult, notably when the coarse grains are of large dimensions.
There is therefore a need for a new sintered product with a coarse structure displaying good mechanical strength, good resistance to thermal shock and a thermal expansion behavior without any notable anomaly.
One aim of the embodiments of the present disclosure is to meet this need.